1. Field of the Invention
The invention relates to a method for producing a coating for an electrode and to an apparatus for producing a coating for an electrode.
2. Description of The Related Art
Battery and battery systems are becoming increasingly important for primary and secondary energy supply purposes. This increasing relevance is greatly influenced by the ever increasing demands for environmental compatibility of the energy supply systems in the sense of emission protection and reusability or recyclability of raw materials and energy.
This firstly applies to the end user and consequently private households and secondly also public installations, where in particular infrastructure and traffic is being equipped with more environmentally compatible energy sources. Already mobile equipment, such as e.g. portable mini-devices, as well as vehicles, especially road vehicles or rail or water vehicles are equipped with environmentally friendly, reusable or rechargeable energy sources in the form of accumulators or batteries. In addition, such energy sources in the form of battery systems are being increasingly used in immobile devices, such as e.g. stand-alone equipment or also as emergency power supplies.
In conjunction with the private end user and also public installations increasing use is being made of metal/air depolarized batteries as rechargeable primary batteries, e.g. in hearing aids or heart pacemakers, as well as in telecommunications engineering and signal installations.
In the further development of existing electrode systems for batteries, battery systems and in particular for rechargeable accumulators or batteries, increasing importance is being attached to the factor of being able to control in a clearly defined, predetermined manner the characteristics of the electrochemically active coating of such electrodes during their primary production. As a function of the intended use, very specific demands are made on the electrode or on the electrochemically active coating of an electrode and in order to fulfill the same specific conditions must be respected at the time of production.
This firstly applies to the surface structure of the electrochemically active coating and secondly e.g. to the specific composition of the electrochemically active coating.
From such primary characteristics of the electrode or the electrochemically active coating result secondary characteristics such as the suppliable energy density, i.e. the ratio of the available energy to the total mass, the environmental compatibility, the possible number of cycles of the rechargeability, the mechanical and/or chemical stability of the battery and in particular the electrodes in the operating or also inoperative state, together with many other physical and chemical charcteristics.
In the production of the electrochemically active coating of an electrode, which is generally carried out in an eletrolytic deposition process, with respect to the possible characteristics of the electrochemically active coating of the electrode very considerable importance is attached to the time pattern of the current and voltage. These electrical parameters determine the deposition and growth rate of the electrode coating.
However, decisive importance is also attached to the composition of the electrolyte, in which the electrolytic deposition process is performed and in particular the change to the electrolyte composition. During electrolytic deposition specific substances are used from and/or delivered to the electrolyte, so that there is a permanent change to the electrolyte composition during the deposition process. In certain circumstances this can considerably influence the quality of the electrochemically active coating of the electrode.
The deposition or growth of the electrochemically active coating can also be influenced by specific material additions in the electrolyte, said electrolyte additions only participating slightly or not at all in the actual deposition, but control the latter.
In order to adjust the concentration of the basic constituents of an electrolyte or the electrolyte additives, hitherto use has essentially been made of mechanical admixing methods, which were aided by time-spaced sampling operations and corresponding concentration measurements.
In such conventional methods for adjusting the concentrations of the individual electrolyte constituents and additives, a significant problem is that such a concentration adjustment can only be performed in an extremely imprecise manner and often with a significant time lag.
Thus, in the conventional adjusting or regulating processes, undesired and often prejudicial concentration fluctuations occurred, which in particular in the case of deposition methods performed in a critical concentration limit range, can often lead to inadequate surface structures or other characteristics of the electrochemically active electrode coating.